class Solution {
    int aim;
    vector<int> path;
    vector<vector<int>> ret;
public:
    vector<vector<int>> combinationSum(vector<int>& nums, int target) {
        aim=target;
        dfs(nums,0,0);
        return ret;
    }

    void dfs(vector<int>& nums,int pos,int sum)
    {
        if(sum==aim)
        {
            ret.push_back(path);
            return;
        }
        if(sum>aim || pos==nums.size())return;
        for(int i=pos;i<nums.size();i++)
        {
            path.push_back(nums[i]);
            dfs(nums,i,sum+nums[i]);
            path.pop_back();
        }
    }
};
